Brushless generators are conventionally formed of a permanent magnet generator, an exciter, and a main generator. Typically, relatively low levels of power are generated by the permanent magnet generator which is made up of a permanent magnet field carried by the generator rotor and which induces electrical energy in a stationary generator output winding. The power from this winding is rectified and subjected to known control parameters before being fed to a stationary field winding of the exciter. The exciter includes an output winding carried by the rotor and as the same rotates within the magnetic field generated by the exciter field winding, electrical energy is induced in the exciter output winding. This energy will be an alternating current and, not untypically, will be three phase alternating current.
The resulting alternating current is rectified by means of a rectifier carried within the rotor and rotating therewith as shown in U.S. Pat Nos. 4,621,210 granted Nov. 4, 1986 and 4,329,603 granted May 11, 1982. The rectified direct current is supplied to the main field winding of the main generator. The main field winding, being carried by the rotor and when energized with direct current and when rotated, provides a rotating magnetic field which in turn induces an alternating current in a stationary main armature output winding. Power thus generated may be taken from the stationary main armature output winding to a point of use by a system that is operative without need for the presence of brushes, slip rings or commutators. In aircraft power generating applications, the generators may be coupled mechanically to the aircraft engine. In the case of jet engines, the coupling is frequently in the engine gear box with the generating system being housed in the same cowling as the engine itself.
The rotating rectifier consists of individual diodes and interconnecting wiring from exciter rotor armature and to the DC main field which is mounted on the rotor shaft. During operation, the electrical losses in the rectifier diodes are dissipated as heat which must be carried away to prevent overtemperature and resulting failure of the diodes. In the prior art, stud mounted diodes have been supported on the exciter rotor hub and cooled by an oil spray while other constructions use a rectifier assembly mounted axially in the generator shaft and cooled by oil flow through the shaft with the leads to and from the rectifier passing through walls of the rotor shaft. Both of these methods of mounting and cooling have significant disadvantages and introduce problems in some instances. Some generators use conduction cooling rather than oil spray cooling to reduce viscous losses in the air gap. The spray oil cooling of the hub mounted diodes frequently results in oil in the air gap and increased viscosity losses. Likewise, the oil leaking through the holes in the shaft, through which the electrical leads pass from the rectifier assembly that is mounted axially between the rotor windings, would be thrown into the air gap causing increased viscous losses. In some designs, there is insufficient annular space for stud mounted diodes on the exciter hub. Other configurations require a drive shaft axially inside of the generator shaft making use of an axially mounted diode package impossible.